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From: Raymond Czaplewski:S28A
Date: ## 02/10/95 13:10 ##
This is an insightful abstract on effects of roads on aquatic systems
in mountainous forests.
Previous comments:
From: Carolyn E. Hidy:R01F14D07A
Date: ## 02/10/95 07:31 ##
Previous comments:
From: Fred B. Samson:R01A
Date: ## 02/09/95 13:57 ##
fyi
Previous comments:
From: Rick Stowell:R01A
Date: ## 02/07/95 09:34 ##
THIS IS A GOOD SUMMARY OF ROAD IMPACTS TO THE ENVIRONMENT. PLEASE
SHARE WITH THE FOLKS IN THE FIELD. THANKS.
Previous comments:
From: Douglas Perkinson:R01F14A
Date: ## 02/07/95 08:48 ##
fyi - our Hydro wrote up a defense of road obliteration for the use
of our IDT's working on fire salvage. Good condensed summary of why
do it to protect stream network.
Previous comments:
From: Steven R. Johnson
Date: ## 02/06/95 14:44 ##
not exaustive, but lots of info and facts. Am sending you a copy of
all references except Wemple, which is bigger and I sent it out a few
months ago anyway. Good luck..... s.
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United States Forest Kootenai NF 506 US Highway 2
West
Department of Service Libby, MT 59923
Agriculture
Reply To: 2500 Date: Feb 6, 1995
Subject: Factors Supporting Road Removal and/or Obliteration
To: Fire Recovery Hydrologists
Hilaire asked me recently to put some thoughts down as to why we, as
hydrologists on the fire-recovery teams, were recommending road removal
and/or
obliteration. It was a question that is coming up frequently now among IDTs
so
I spent a some time thinking about the subject and offer the following for
you
to use as you see fit when questions about roads, road problems, and road
obliteration objectives come up:
NOTE: The articles mentioned herein are by no means complete as to the amount
of available information on the subject. However, I believe they provide
enough information to explain why I believe road removal and/or obliteration
should be emphasized, on a case by case basis, for the fire salvage analyses.
ROADS AND FOREST HYDROLOGY- Roads have been identified as the major impact on
the forest environment. Literally hundreds of publications in the last 10-20
years have brought this out. California analyzes cumulative watershed
effects
in NEPA documents using the Equivalent Roaded Area concept, much the same as
we
use the Equivalent Clearcut Area concept. They do this because they realize
roads are the phenomenon of change in their environment, so they relate all
activities to that one.
These impacts from roads basically fall into three areas: introduced sediment
into streams; snowmelt re-direction and concentration; and surface flow
production. Each is briefly documented in this paper.
INTRODUCED SEDIMENT- This one is pretty obvious so I won't spend a lot of
time
on it (entire books have been written on the subject, including one by the
EPA
several years ago). However, I need to mention that road surface drainage,
and
the sagging of road ditches into channels and creeks, continues to be the
most
common BMP violation we have on this forest. Roads designed in the past, the
very ones we are trying to obliterate now, were designed without current BMP
philosophy in mind so it is not surprising. For the roads we no longer
actively use, our dwindling road maintenance budget will make it difficult to
maintain the culvert crossings. When these fail during storm and runoff
events, tremendous amounts of sediment can be delivered directly to the
channel
and from there down into lower streams with significant beneficial uses such
as
sensitive fish habitat. It is important to note that culverts can fail if
not
maintained even on roads that have become so brushed in that travel is
difficult. Even on roads that appear to be so thick with alder that a
sediment
production concern seems ludicrous, we often find that the road tracks are
still actively functioning as erosion sources. True, it is not the
magnitudeit was when the road was constructed, but it is still an erosion
source that
comes into play during events when we also have plenty of flow to take the
erosion on into a channel.
SNOWMELT RE-DIRECTION AND CONCENTRATION Roads are basically a horizontal
feature in a landscape driven by vertical, gravity driven processes. Spring
snowmelt and runoff from our frequent mid-winter melt and rain-on-snow events
that would normally travel in a downhill direction, usually as shallow
sub-surface flow, is intercepted by the compacted roads and their ditches and
becomes surface flow. By doing this they are, in effect, dramatically
increasing the drainage efficiency of a watershed. Increasing the drainage
efficiency of a watershed concentrates flow so that peaks are higher. A
recent
Oregon State University Thesis by Wemple under the direction of Gordon Grant,
focused on the hydrologic interaction of forest roads with stream networks.
In
this document they clearly point out the contributions of the road and ditch
network to peak flows. They suggest that the roads in their study might have
extended the stream network by as much as 40% during storm events. Couple
this
fact with information from a USGS study by Carlston that found that the mean
annual flood varies with stream density in the form of Q/mi_2_ = 1.3 D_2_,
where Q
is flow and D is drainage density. Using Wemple and Grants' finding of a 40%
increase in drainage density and applying it to this equation, we find that
the
flow would almost double (1.96 times) using an average figure from their
work.
They found these results in two watersheds where the road density was only
1.61
mi/mi_2_. In many of our watersheds, and particularly in ones where we are
trying to remove or obliterate older roads, we have densities of roads,
average watershed on this forest is probably double their average, and the
heavily harvested ones probably triple or more. Thus our efficiency increase
would be expected to be even higher.
In another study which documents this phenomenon, Hollis examined the effect
of
basin urbanization on flood recurrence intervals. While this may sound like
it
does not apply, I believe it does because he found that the development of a
storm water drainage system which increased the drainage efficiency of the
basin was involved. In his analysis he also used information from Leopold
relating floods to the percentage of the area that was impervious.
Hollis found dramatic increases in the size of floods: small floods may be
increased 10 times; and the 100-year flood may be doubled in size when
drainage
is basin-wide and 30% has been paved (left with impervious surfaces). In our
basins on this forest, we are talking about a road network that functions as
the efficiency improvement, and harvest units and road surfaces that function
as impervious or reduced infiltration areas, so I believe their work is very
applicable.
Studies by Dennis Harr have consistently pointed out the effects of the
compacted surfaces (roads, skid trails, landings, and firelines) on peak
flows. In the watersheds he has studied, he has found significant peak flow
increases when only 6% of the watershed was compacted, and numerous authors
have used Harr's data to claim that a 12% threshold exists (believing that
keeping compacted surfaces below 12% will protect channels from the effects
of
peak flows). While pointing out the fallacy of the "12% threshold", Harr
does
emphasize that building and locating roads so as to not intercept and
re-direct
water is very important.
Burroughs et al in the Bitterroot Mountains (Volume of Snowmelt Intercepted
by
Logging Roads); and King and Tennison at Horse Creek (Alteration of
Streamflow
Characteristics Following Road Construction in North Central Idaho) have all
documented the effects of roads on the normal drainage phenomenon on forested
slopes.
SURFACE FLOW PRODUCTION Roads in our glacially-modified environment actually
produce water: Infiltration rates in glacial soils are not high, particularly
more than a few feet below the loess/till interface. Road cuts that exceed a
few feet in height take shallow subsurface water and convert it to surface
flow, adding it to a ditch where it becomes part of a peak flow event.
Publications by Megahan (Subsurface Flow Interception by a Logging Road in
Mountains of Central Idaho), and the King/Tennison article mentioned above
all
relate to the surface flow developed by roads. Based on the observations of
Hydrologists and the Soil Scientist, the KNF used a factor of 1.3 in the old
Kootenai Water Yield Model to indicate that we believed roads produced 1.3
times the flow of a normal clear-cut unit. We did not have the hard data to
back this number up, but it looked reasonable.
A few years ago the Flathead NF developed data to substantiate this number.
They investigated a large harvest area that had very few channels but which
was
having a problem keeping pipes in place: they were being consistently
over-topped and blowing out. They discovered that the road cuts were
intercepting shallow sub-surface flow and converting it to surface flow that
was then being routed to channels and culverts at road crossings. They sent
a
crew out to actually gage the flow in the ditches being produced by the
interception. They found that amounts varied by soil material, as expected,
but also found that the flow volumes, in FT_3_/second, were amazing. The
Flathead data is summarized below:
CFS PER MILE OF ROAD
SOIL MATERIAL AVERAGE RANGE
Fine sandy till 3.7 1.1 - 8.4
Lacustrine till 1.6 0.5 - 15.3
Residual Upland 1.6 0.5 - 5.8
--------------------------------------------------------------------
Interpretation: In basins with average road densities, on the order of 4+
mi/mi_2_; and the average flow production rates listed in the table, we can
have
between 6 and 15 cfs of water added to the natural amount for every square
mile
in the basin. Based on the upper end of the measured ranges of surface flow
generation, we could have up to 61 cfs per square mile of drainage basin. It
is easy to see why the Flathead was blowing out their crossings.
In portions of our forest, where we have the road densities mentioned above
(10-20 mi/mi_2_) and substantially more precipitation than this area of the
Flathead, we have had similar problems with crossings. To our credit we have
consistently sized our culverts larger than would the Flathead, but the
discussion still points out the volumes possible and the hazards involved
with
road interception of shallow sub-surface flows. Removing or obliterating
roads
so that the flow would remain sub-surface is a major benefit of the proposals
we are suggesting.
THE BOTTOM LINE We have many watersheds on this forest, including most
within
the fire salvage analysis areas, where water yields from past events are
already stressing or damaging the aquatic system. Roads, through their
interception and re-direction of sub-surface runoff, have had a major
contributing emphasis. Restoration of the normal drainage phenomenon can be
achieved through the use of road removal and obliteration. In fact, Wemple
concludes that modifying road segments is the most effective way to approach
watershed restoration.
Also, in the Purpose and Need Statements for Salvage Projects in these areas,
we need to explain why salvage activities will lead to an improvement in
watershed condition. For streams listed on the Montana TMDL (water quality
limited) list; for watersheds we have identified as being in degraded
conditions even before the fire; and in watersheds that we know were in
experiencing problems, it is absolutely critical that we be able to show that
our activities are a plus. In the case of the TMDL-listed streams, the State
Water Quality Division has told us we cannot cause any increases in listed
problem parameters, which usually include sediment. Showing a decrease in
sediment while we salvage log will require us to show a decrease elsewhere in
the watershed so the net change is in the positive direction. A reduction in
total road mileage through obliteration will enable us to show this
improvement. If we cannot show an improvement, we stand little if any chance
of having regulatory agency approval for salvage activities, regardless of
our
assertion that we will use generated funds for watershed rehabilitation.
STEVEN R. JOHNSON
Forest Hydrologist
attachments: references used
REFERENCES (copies of all but Wemple attached [provided earlier])
Burroughs, E.R, Jr., M.A. Marsden, and H.F. Haupt, 1972. Volume of Snowmelt
Intercepted by Logging Roads. Journal of the Irrigation and Drainage
Division,
Proceedings of the AMSCE.
Carlston, C.W., 1963. Drainage Density and Streamflow. US Geological Survey
Professional Paper 422-C, Physiographic and Hydraulic Studies of Rivers.
Harr, R.D. 1986. Myths and Misconceptions about Forest Hydrlogic Systems and
Cumulative Effects. Paper presented at California Watershed Management
Conference Nov 18-20, 1986, Sacramento, California.
Hollis, G.E. The Effect of Urbanization on Floods of Different Recurrence
Intervals, 1975. Water Resources Research, Vol 11, No.3, pages 431-435.
King, J.G. 1989. Streamflow Responses to Road Building and Harvesting: a
Comparison with the Equivalent Clearcut Area Procedure. USDA, FS Research
Paper
INT-401.
King, J.G., and L.C.Tennison. 1984. Alteration of Streamflow Characteristics
Following Road Construction in North Central Idaho. Water Resources Research,
Vol 20, No. 8, pages 1159-1163.
Megahan, W.F. 1972. Subsurface Flow Interception by a Logging Road in
Mountains
of Central Idaho. AWRA, National Symposium on Watersheds in Transition, pages
350-356.
Wemple, B.C., 1994. Hydrologic Integration of Forest Roads with Stream
Networks
in Two Basins, Western Cascades, Oregon. Oregon State University MS Thesis.
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